Interpretive Summary: Beauveria bassiana is a naturally-occurring fungus that causes disease in the western tarnished plant bug. When field collected plant bugs are reared in the laboratory, they are sometimes accompanied by this disease. Introduction of disease into laboratory insect colonies usually necessitates disposal of the colony and disrupts research efforts. We examined the use of germicidal ultraviolet light (UV-C) for maximizing the potential of maintaining a disease-free plant bug colony. Less than 7 minutes of exposure to a laboratory UV-C lamp killed more than 99% of Beauveria spores. When plant bug adults, previously treated with Beauveria, were exposed to the lamp for 2 hours, incidence of the disease was greatly diminished but not eliminated. This 2-hour exposure had no discernible effect on later mating or reproduction by the plant bugs. Our results suggest routine exposure of field-collected plant bug adults to UV-C light may reduce the probability of introducing Beauveria and other diseases into laboratory colonies without adversely affecting the insects.

Technical Abstract:
The western tarnished plant bug, Lygus hesperus Knight, is an important pest of crops in the western U.S. Research on the basic biology of L. hesperus often relies on access to healthy insects, which are typically provided through laboratory cultures. However, maintenance of colony vigor often requires periodic introductions of field-collected specimens or re-initiation of the colony. Either approach poses a risk of introducing diseases with the field-collected insects. We examined the potential utility of exposure to ultraviolet light (UV-C) as a means of sterilizing adult L. hesperus previously treated with spores of Beauveria bassiana (Balsamo) Vuillemin, and also examined the influence of exposure to UV-C on subsequent lygus reproduction. Mortality of B. bassiana conidia increased rapidly with increased exposure to UV irradiation, which also delayed germination of conidia at exposure times >2 min. Based on assays conducted 48 h after UV exposure, 6.45 min of exposure to UV-C (130 microwatt/square cm) reduced germination of conidia to approximately 1%. When L. hesperus adults treated with B. bassiana were exposed to UV-C for 2 h, infection by the pathogen was greatly decreased but was not eliminated. Similar exposure of untreated L. hesperus adults did not reduce subsequent fecundity. Our results suggest routine exposure of field-collected L. hesperus adults to UV-C irradiation may reduce the probability of introducing B. bassiana into laboratory colonies with little or no adverse reproductive consequences.